Field of the Invention
The present invention relates to a two-component system for preparing polyurethane foam.
Introduction
Polyurethane foams prepared using poly(methylene diphenyl diisocyanate) (PMDI) having a functionality of 3.0 or less suffer from having low thermal insulation properties relative to foam prepared from PMDI having a functionality greater than 3.0. Nonetheless, it is desirable to prepare thermally insulating foam using PMDI having a functionality of 3.0 or less because lower functionality PMDI is less expensive to obtain than higher functionality PMDI.
U.S. Pat. No. 4,791,148 discloses a method for increasing the thermal insulating properties (decreasing the thermal conductivity properties) of polymeric foam by reacting a pre-polymer reaction product of a polyester polyol and isocyanate with a polyol.
U.S. Pat. No. 5,064,873 discloses a method for producing foam having increased thermal insulating properties by reacting a pre-polymer of an isocyanate and a polyol with a polyester polyol. The polyol used to prepare the pre-polymer must have a low free glycol content (less than about 7 weight percent based on total polyester polyol weight) in order to achieve the improved foam insulation value.
It would advance the art of thermally insulating polymeric foam to discover how to prepare thermally insulating foam using a PMDI with a functionality of 3.0 or less. At the same time it would further advance the art if the solution did not require a pre-polymer of a polyester polyol or a polyol having less than 7 weight-percent free glycol content based on polyol weight.